Hypertension and antihypertensive therapy
Induction of anesthesia constitutes one of the more serious threats to circulatory stability. In addition to possible direct effects of anesthetic agents on the cardiovascular system, the mechanisms of cardiovascular control are also distributed during that time. Baroceptor sensitivity is altered, sympathetic activity is either depressed or reflexly increased, and autonomic input from various sources can be activated by different surgical and anesthetic manipulation. The results of this complex interplay of factors can be either a severe hypotension or a marked hypertension; the former was often stressed in the past. More recently, the frequency, complexity, and dangers of the latter are being more widely recognized.
Of particular importance in this setting is the question of antihypertensive therapy and the advisability of its discontinuance before surgery. Anti-hypertensive drugs are of different types; hence, one cannot indulge in generalizations regarding their use. A few years ago sympatholytics were mostly used. The spectrum of antihypertensives is much wider now. Conventional discussions regarding antihypertensive therapy during anesthesia must therefore be viewed in that context. Classic viewpoints were greatly influenced by the sympatholytics in use in the past. The contractility of the isolated heart is severely depressed by most anesthetic agents, but this is counterbalanced in intact organisms by reflex sympathetic activity. Undue depression of adrenergic activity was therefore judged undesirable in diseased hearts, which are more dependent than normal on this drive for adequate performance. Under these conditions, a case could be made for the preoperative discontinuance of drugs that could interfere with autonomic . . .